FR2706901A1 - - Google Patents

Abstract

The invention describes a curable coating composition based on silica and acrylate, free of gel, prepared from one or more components of soluble salts, soaps, amines, nonionic and anionic surfactants, acids or mixtures thereof, and a process for the preparation of such compositions.

Description

Process for the production of curable coatings The present

  the present invention relates to curable coating compositions and a process for the preparation

  frost-free curable coating compositions.

  More particularly the present invention relates to a gel-free curable coating composition, based

silica and acrylates.

  Curable coating compositions based on silica and acrylate resins are generally prepared

  using colloidal silica. It is desirable to pro-

  coating a dried coating, by removing water from the colloidal silica by azeotropic distillation, using a compatible solvent, for example isopropyl alcohol, and obtaining the treated silica in an acrylate support

  reagent. It turns out that when you do this

  tion under a nitrogen atmosphere, a gel forms at some point during the extraction process, when almost all of the compatible solvent is removed. It is known that highly reactive acrylates require

  oxygen so that gelation is avoided, and therefore

  sequence this dewatering operation - was normal -

  ment carried out under at least a certain amount of oxygen

  uncomfortable. Due to the flammability of the solvents compared

  It is highly desirable to carry out these reactions.

  without the addition of oxygen. In addition, in reci-

  normally used extraction clients, it is difficult 2- to ensure adequate dispersion of the oxygen. The process of the present invention is a process for the preparation of curable, gel-free coating compositions which do not require the addition of oxygen to the system. In addition, it has been found that coating compositions thus dried exhibit longer shelf lives.

  The term "frost-free" means compounds

  coating conditions in which the viscosity is adjusted

  ted within usable limits. The viscosity will vary naturally.

  actually depending on the specific polymers, however, when the composition is diluted in a suitable solvent,

  practically no undissolved substance remains.

  US-A-4,486,504 and 4,455,205 relate to formulas-

  hard coating compositions curable with

  UV rays, and resistant or not to atmospheric agents.

  US-A-4,973,612 (Cottington et al.) Relates to coating compositions which contain polyfunctional acrylates, unsaturated organic compounds and

  aqueous dispersions of colloidal silica.

  US-A-4,644,077 (Gupta) relates to a process for the

production of organophilic silica.

  US-A-4,491,508 (Olsen et al.) Relates to a process for the preparation of a hard coating composition without

  solvent, which may be useful in the present invention.

  US-A-4,478,876 (Chung) relates to a coating process

  ment of a support with a composition curable with

  UV rays, and conferring resistance to abrasion. This pro-

  yielded concerns the formation of the composition under an atmosphere

non-inert sphere, such as air.

  In general, the above patents describe coatings

  which can be improved by the process of

present invention.

  US-A-5 120 811 (Glotfelter et al.) Relates to an organic / inorganic surface coating (epoxy / glass) -3-

  wear-resistant, on a transparent protective layer,

  excellent protection against stains and excellent conservation of gloss. A hydrolyzed silicate

  under acidic conditions is combined with a coating agent

  silicone type range hydrolyzed under acidic conditions, an epoxy monomer, a photoinitiator and a surfactant based on silicone oil, but without the use of silica

  colloidal or acrylate monomer.

  US-A-5 103 032 (Turner et al.) Relates to compounds

  sitions containing an acryloxysilane or a methacryloxysilane and an N, Ndialkylaminomethylene-phenol, in an amount at least sufficient to prevent polymerization of the silane

  during its formation, its purification and its storage

  kage, but there is no mention of the use of

colloidal silica.

  US-A-4,831,093 (Swarts) relates to the polymerization of methyl methacrylate with an initiator consisting of a perester salt of maleic acid, using an activator of the bisulfite type in water-in-oil emulsion , but in the absence

of SiO2.

  US-A-4,780,555 (Bank) relates to a process for the preparation of acrylic-functional halosilanes, by reacting a halosilane with a compound

  organic with acryloxy or methacryloxy functionality, pre-

  sence of a hydrosilation catalyst based on platinum and a stabilizing amount of phenothiazine, in which the reaction mixture is brought into contact with an inert gas containing oxygen. No use of salt or

surfactant is suggested.

  US-A-4,709,067 (Chu et al.) Relates to a process

  improved for preparation, purification and / or storage

  kage of organosilicon compounds containing meth-

  acryloxy or acryloxy, without the undesirable polymerization which is normally associated with methacrylate linkages. No

  salt or surfactant is not suggested to inhibit this polymer

  -4 - rization, and polymerization in this case is associated with

methacrylate bonds.

  US-A-4,021,310 (Shimizu et al.) Relates to a process for preventing the polymerization of acrylic acid or acrylic esters during distillation for the separation or purification of the acrylic acid obtained by catalytic vapor phase oxidation of propylene or acrolein, or acrylic esters derived from said acrylic acid. Colloidal silica is not mentioned, and the polymerization prevented is that of acrylic acid

or acrylic esters.

  US-A-3,258,477 (Plueddemann et al.) Relates to alkoxysilanes and compositions thereof, and does not describe

  not the use of colloidal silica.

  The present invention relates to a curable coating composition comprising a compound selected from soluble salts, soaps, amines, nonionic and anionic surfactants, acids and bases, and mixtures thereof, and a process for the preparation thereof. preparation of curable, gel-free, silica and acrylate-based coating compositions, in which such a compound

  is added to the reaction mixture, before devolatilization

  tion. The curable coating compositions of the present invention are obtained from a composition

  gel-free, silyl-based curable coating

  acrylate, comprising a compound chosen from salts

  soluble, soaps, amines, anio-surfactants

  acids and nonionics, acids and bases, or

mixtures of these.

  Silylacrylate type resins are known in

the technique.

  The silylacrylate of the present invention can generally be represented by the following formula:

(R) R O R2

  ) a 2 12 3 o 2 (1) (R'O) 4_abSi [C (R) 2CHR OC-C = C (R) 2] b To obtain the resins used in the present invention, an acrylic monomer is added to the silylacrylate of formula: O

2 2 I2 4

(2) [(R) 2C = CR -C-O] nR4

  Each radical R is independently an organic radical.

  monovalent nique in C1_13, each radical R 'is independent

  a C 8 'alkyl radical R is chosen from a hydrogen atom, R or mixtures thereof, each radical R 3

  is independently a C1-8 alkylene radical each

  cal R is independently a mono- or polyvalent organic radical, a is an integer worth from 0 to 2, limits included, b is an integer worth from 1 to 3, the sum of a + b is equal to 1-3, and n is an integer equal to

from 1 to 6, limits included.

  If desired, we can add a UV photo-initiator

  to the resulting mixture of the silylacrylate and the acrylic monomer

lique.

  In formula (1), each radical R is more particular

  especially a C1_8 alkyl radical, such as methyl, ethyl, propyl, butyl and the like. An aryl or halogenated aryl radical, for example the phenyl, tolyl, xylyl, naphthyl, chlorophenyl and the like radical; each radical R1 is more particularly, for example, any one of the C1-8 alkyl radicals included in the definition of R; and the radicals included in the definition of each of the radicals R2 are hydrogen atoms and each of the radicals included in the definition of R. R3 is more particularly a divalent alkylene radical, by

  example the methylene, ethylene, trimethylene, tetra- radical

  methylene and the like. The divalent organic radicals included in the definition of R4 are radicals R3, branched C28 alkylene radicals, halogenated and branched C28 -6-alkylene radicals, hydroxylated and branched C28 alkylene radicals, branched acrylate radicals,

  C6-13 'arylene radicals for example, phenyl radicals

  lene, tolylene, naphthylene and the like, aryl radicals

  halogenated C6_13 lene, and the like.

  Formula (2) includes poly- acrylate monomers

  functional, for example diacrylates of formulas:

CH3 CH3

CH2 = COO-CH2-OOCC = CH2

CH = CHCOO-CH2-CH2-OOCCH = CH2

CH2 = CHCOO-CH2-CHOHCH2-OOCCH = CH2

CH3 CH3

CH2 = COO- (CH2) 6-OOCC = CH2

CH2 = CHCOO- (CH2) 6-OOCCH = CH2

OOCH = CH2

CH = CHCOO-CH2-CH2-CH-CH3

CH3

CH2 = CHCOO OOCCH = CH2

Br

CH2 = CHCOO OOCCH = CH2,

  -7 - and the like and triacrylates of formulas:

OOCCH = CH2

CH2 = CHCOO-CH2CH2CHCH2-OOCCH = CH2

CH2 = CHCOO-CH2

CH2 = CHCOO-CH2-C-CH2CH3

CH2 = CHCOO-CH2

CH20H

CH2 = CHCOO-CH2-C-CH2-OOCCH = CH2

CH2-OOCCH = CH2

CH3

CH2 = CHCOO O OOCH = CH2,

  and the like and tetraacrylates of formulas:

CH2 = CHCOOCH2

CH2 = CHCOO-.H2-CH-CH2-OOCCH = CH2

H3 = CHCOOCH2

  OH CH2 = CHCOO-CH2CHCH-CH2CH-OOCCH = CH2, etc.

CH2 = CHCOO-CH2 CH2-00CCH = CH2

  The silylacrylates of formula (1) include compounds of formulas: -8 - CH2 = CCH3CO2-CH2CH2-Si (OCH2CH3) 3, CH2 = CHCO2-CH2CH2- Si (OCH3) 3, CH2 = CCH3CO2-CH2CH2CH2-Si (OCH2CH3) 3, CH2 = CHC02-CH2CH2- Si (OCH2CH3), CH2 = CCH3CO2-CH2CH2CH2-Si (OCH3) 3, CH2 = CHCO2-CH2CH2CH2- Si (OCH3) 3, CH2 = CCH3CO2-CH2CH2CH2-Si (OCH2CH3) 3, CH2 = CHCO2-CH2CH2CH2- Si (OCH2CH3) 3, CH2 = CCH3C02-CH2CHC2CH2-Si (OCH3) 3,

CH2 = CHC02-CH2CH2CH2CH2-SI (OCH3) 3,

  CH2 = CCH3CO2-CH2CH2CH2C- H2-Si (OCH2CH3) 3,

  CH2 = CHCO2-CH2CH2CH2CH2-Si (OCH2CH3) 3, and the like.

  Colloidal silica, which is another component of the curable coating composition of the present invention, is a dispersion of silica (SiO2) particles smaller than one micrometer in size, in an aqueous medium or other solvent. Silica provides silicon atoms

  tetrafunctional (Q) and adds hardness to coatings

  ment. When mixed with trifunctional acrylates

  containing silicon (T), Q / T mixtures are formed.

  Colloidal silica dispersions are available from chemical manufacturers such as DuPont

  and Nalco Chemical Company. Colloidal silica is available

  nible in acid or basic form. However, for the purposes of the present invention, it is preferable to use the acid form. It has been found that it is possible to achieve superior properties of hard coatings with acid colloidal silica (i.e. low dispersions

  sodium content). Alkaline colloidal silica can also

  be converted to acid colloidal silica with addi-

  acid such as HCl or H2SO04, together with

strong agitation.

  Nalcoag 1034A, available from Nalco Chemical

  Company, Chicago Ill. (USA) is an example of colloidal silica

  satisfactory for use in these compounds

  -9- coating. Nalcoag 1034A is an aqueous dispersion of colloidal silica at acid pH, of high purity, having a low Na 2 O content, a pH of approximately 3.1 and a sio 2 content of approximately 34% by weight. In the examples given below, the weight in g or parts by weight of the colloidal silica comprises its aqueous medium. So by

  example, 520 g of Nalcoag 1034A colloidal silica shown

  smell about 177 g of SiO2 by weight. Note, however, that the aqueous medium is a convenient means of handling

  colloidal silica and is not a necessary part

  of the curable coating composition of the pre-

  invention. However, since water is

  required for the hydrolysis of SiOR, a cer-

  a lot of water with non-aqueous colloidal silica.

  The expression "colloidal silica" is intended to represent a wide variety of forms of finely SiO2

  which can be used to form the composi-

  The curable coating compositions of the present invention without the need for excessive experimentation. We will be able to

  find a more detailed description in US-A-4,027,073,

incorporated here by reference.

  The coating compositions of the present invention

  can be formulated without any additional hardener

  to hush up. If desired, the coating compositions

  can be hardened by exposure to an electron beam

  trons (FE). In the case of exposure to an FE, it is desirable to have a thin coating. This coating has

  preferably less than 2.5 cm thick, and preferably

less than 25 gm.

  This composition can also be formulated for

  contain hardeners. One such hardener is a photo-

  initiator. The composition can then be hardened by exposure.

  tion to a UV light source. It is desirable to have a coating having a thickness of about 2,500 mm, and

  preferably less than about 25 mm.

- 10 -

  Although the coating compositions may

  contain only one of said polyfunction acrylate monomers-

  nels, the preferred coating compositions contain a mixture of two or more polyfunctional monomers, preferably a diacrylate and a higher functionality acrylate. In addition, small amounts of monoacrylate can be used in special cases. Furthermore,

  the UV curable compositions of the present invention

  tion may contain nonacrylic organic monomers

  Aliphatic unsaturated, radiation curable

  UV, in proportions of up to 50% by weight of the compounds

  coating materials curable with UV rays, which

  take, for example, substances such as N-vinyl-

  pyrrolidone, styrene, mixtures of vinyl ether / maleate, trifunctional and tetrafunctional acrylates,

and the like.

  Coating compositions which include a

  mixture of diacrylates and acrylates with superior functionality

  higher have a ratio of diacrylates to acrylates to function

  higher quality generally ranging from about 0.5: 99 to about 99: 0.5, and even better from about 1:99 to about

  99: 1. As examples of mixtures of diacrylates and acrylates,

  lates with higher functionality, there may be mentioned mixtures of hexanediol diacrylate and triacrylate

  trimethylolpropane, hexanediol diacrylate and tri-

  pentaerythritol acrylate, hexanediol diacrylate and dipentaerythritol pentaacrylate, diethylene glycol diacrylate and pentaerythritol triacrylate, and

  diethylene glycol diacrylate and tri- triacrylate

  methylolpropane. Coatings containing the photoreaction product of two polyfunctional acrylate type monomers are preferred. Likewise, the coatings may contain the ultraviolet light reaction product of a single polyfunctional acrylate monomer. Preferably,

- l1 -

  both a diacrylate and an acrylate with superior functionality

  better. A preferred high functionality acrylate is

  trimethylolpropane triacrylate. We prefer the

  sitions comprising between 0.2 and 99 parts by weight of tri-

  trimethylolpropane acrylate, before or after hardening.

  Also preferred are cured compositions comprising from about 2 to about 99 parts by weight of trimethylolpropane triacrylate. The photocurable coating compositions also contain a photosensitizing amount of photoinitiator, i.e., an amount effective for

  photocuring the coating composition

  is lying. This amount generally represents from about 0.01 to about 15 parts by weight, and preferably from about 0.1 to about 10 parts by weight, relative to the total weight of the colloidal silica, of the condensation reaction product. and of hydrolysis of a silylacrylate of formula (1) and of a

acrylate monomer of formula (2).

  As indicated in US-A-4,491,508, certain mixtures of ketone-type and hindered-amine-like substances

  sterics are effective photo-initiators for reticula-

  tion of the coating compositions described above, in air, to form suitable hard coatings, after exposure to UV radiation. This patent is incorporated here

by reference.

  A ketone type photoinitiator used is a, "-

  diethoxyacetophenone. A preferred photoinitiator is methyl benzoylformate, having a molecular weight of 164, and used in an amount of 5 parts by weight or more. A, 7 parts by weight of methyl benzoylformate, an amount of photoinitiator corresponding to 50 mol% is available additionally in the formulations relative to the percentage by mol available when 5 parts by weight of x are used, molecular weight diethoxyacetophenone

- 12 -

  higher. Methyl benzoylformiate is available under the name Vicure 55 from Akzo Chemicals Inc., Chicago, Illinois (USA). According to one embodiment

  of the present invention, 35 mmol of photo-

  initiator per 100 g of coating composition. A greater variety of supports can be coated when a higher proportion of photoinitiator is used. Photoinitiators dissociate into free radicals when exposed to UV light. The free radicals then cut the double bonds between the carbon atoms in

acrylate groups.

  The amount of photoinitiator added to the compounds

  tions is more than 5 parts by weight, compared to

  parts by weight of non-volatile components: silica col-

  loïdale, product of condensation and hydrolysis reaction of a silylacrylate of formula (1) and of an acrylate monomer of formula (2). Preferably, between 5 and about 12 parts by weight are used when the photoinitiator is methyl benzoylformate. Even better, between about 6 and about 7% by weight of methyl benzoylformate is added.

  The use of larger amounts of photo-

  initiator provides curable coatings with shorter cure times. These curable coatings are particularly useful and desired for the application of films at high speeds. Current film application-curing rates range from about 9.15 to 5.5 meters per minute (mpm). However, according to this

  invention, higher durational speeds can be obtained

  cementation, since high amounts of photo-

  initiator allow faster curing. Coatings

  films, including hard coatings

  scissors of the present invention, can be cured by passing under a UV light source, at speeds ranging

  15.25 to 152.5 meters per minute, if you use enough

- 13 -

  ment of light sources. At such high speeds and under such conditions, the curable coatings of the prior art would remain less cured, as would

  would manifest as softer coatings.

  The coating compositions of the present invention

  may optionally also contain stabili-

  UV absorbers or sorbents, such as resorient monobenzoate

  nol, 2-methyl dibenzoate and resorcinol, and the like

  laires. The stabilizers may be present in a pro-

  portion, relative to the weight of the coating compositions

  ment, to the exclusion of any additional solvent which may possibly be present, ranging from approximately 0.1 to parts by weight, preferably from approximately 3 to approximately 18 parts by weight, relative to the colloidal silica and to the product condensation and hydrolysis reaction of a silylacrylate of formula (1) and of an acrylate monomer of formula (2). The UV curable coating composition may contain from about 1 to about 25 parts by weight of stabilizers based on the colloidal silica and the condensation and hydrolysis reaction product of a silylacrylate of formula (1) and d '' an acrylate monomer of

formula (2).

  Suitable solvents include an alcohol mis-

  target with water or any water-solvent azeotrope. Examples of solvents that may be mentioned are isopropyl alcohol (IPA), 4-methoxypropanol, n-butanol, 2-butanol,

ethanol and the like.

  Suitable compounds which can be added to the curable compositions can include soluble salts, soaps, amines, non-surfactants

  ionic and anionic, acids, bases and the like.

  The compositions for use in the present invention include any compound which prevents gel formation in the coating compositions of the present invention. The specialist will agree that it is possible

- 14 -

* to use any compound of this type, insofar as it does not precipitate colloidal silica and insofar as properties such as curing speed, hardness, resistance to atmospheric agents and protection of the support are maintained at suitable degrees. A com-

  preferred is sodium acetate.

  Examples of soluble salts include stannous chloride, sodium acetate, sodium bicarbonate, tetrabutylammonium acetate, tetrabutylammonium bromide and the like. As examples of soaps contemplated for use in the present invention,

  mention may be made of calcium neodecanoate, standard octoate

  neux, zinc octoate and the like. The amines contemplated for use in the present invention include triethylamine. As examples of non-surfactants

  ionic and anionic, there may be mentioned secondary alcohols

  linear ones having from about 11 to about 18 carbon atoms, having reacted with polyoxyethylene-oxypropylene (OEOP) z, z being worth from 8 to 10; nonylphenol, octylphenols having from about 3 to about 10 EO groups;

  an alkylphenol- (OE) 70H; secondary alcohols with

  about 11 to about 18 carbon atoms, with (OE) xH, x being from about to about 10; HO (OE) x (OP) y (OE) xOH, x being from about 2 to about 100 and y being from about 2 to about 100; ammonium laurylsulfonate; and the like. Examples of acids contemplated for use in the present invention include hydrochloric acid and

  similar. Specific bases may include tri-

  ethylamine and the like. The specialist will recognize that

  these are purely representative examples, and it is pos-

  likely to use other compounds as well as a combination

of those indicated above.

  Compounds for use in the preparation of

  sente invention include all compounds which prevent gel formation in the coating compositions of the

- 15 -

present invention.

  The amount of the compound present in the compositions of the present invention is an amount sufficient to maintain the viscosity of the mixture to such an extent that when diluted in a suitable solvent, there remains

no undissolved substance.

  The coating compositions of the present invention

  tion may also optionally contain various spreading agents, surfactants, thixotropic agents, stabilizers with respect to UV light, stabilizers with respect to

  hindered amine type light, and dyes.

  All of these additives are well known in the art and

  need not be described in more detail. Therefore

  only a limited number will be mentioned, it being understood that any of these compounds can be

  used, as long as they do not harm the photo-

  curing coating compositions and do no harm

  not the non-opaque nature of the coating.

  Various surfactants, including surfactants

  anionic, cationic and nonionic active agents are described in the Kirk-Othmer Encyclopedia of Chemical Technology, vol. 19, Interscience Publishers, New York, 1969, p. 507-593 and in the Encyclopedia of Polymer Science and Technology, vol. 13, Interscience Publishers, New York, 1970,

  p. 477-486, both of which are incorporated herein by reference

  rence. In addition, flow regulators and spreading agents, such as BYK300 and BYK310 from BYK Chemie, Wallingford, CT (USA) can be added in amounts ranging from 0.01 0 6 parts by weight, based on the colloidal silica and to the condensation reaction product and

  hydrolysis of a silylacrylate of formula (1) and of a mono-

mother acrylate of formula (2).

  In general, the process of the present invention is carried out in an atmosphere which is practically free of oxygen. "Virtually oxygen-free" means

- 16 -

  that the atmosphere generally contains less than 15% and

  preferably less than 10% oxygen. Even better, the atmos-

  sphere contains less than 6% oxygen.

  It is therefore recognized that the compounds can be added to the curable coating composition based on silylacrylate at any time during the process of the present invention. The compounds can be added before or after the preparation of the Q / T resin mixture. The specialist will also recognize that other formulations

  above mixtures may be required or desired

tables.

  The present invention is illustrated by the examples

  descriptive and non-limiting below.

EXAMPLE 1

  A masterbatch of hydrolyzate was prepared as follows:

  13.0 parts of methacryloxypropyltri-methoxysilane were hydrolyzed in 86.9 parts of acid colloidal silica (Nalco 1034A)

  0.07 parts of p-methoxyphenol and 464 parts of isopropyl alcohol (IPA), and about 73% of the water and IPA was removed. This substance contained 24.2% by weight of non-volatile component and was used as the silicon fraction for all the reactions described in the

table 1.

- 17 -

Table 1

  Quantity Quantity 1 2 (ppm of g / 161.2 g Viscosity 2 Ex. Hydrolyzate product at 25 C n Devolatilized compound at 24.2% mm2 / s 1 Control 0 0 Gel 2 Stannous chloride 133 0.0100 40.5 3 Sodium acetate 213 0.0160 40.1 4 Sodium acetate 52 0.00396 41.5 Sodium acetate 40 0.00297 41.5 6 Sodium acetate 30 0.00205 247 7 Sodium acetate 100 0.00733 39 , 5 8 Sodium bicarbonate 110 0.0082 41.9 9 Tetrabutylammonium acetate 133 0.01000 41.4 Tetrabutylammonium bromide 200 0.0150 Low 11 Calcium neodecanoate 213 0.0160 41.6 12 Stannous octoate 533 0.0400 Low 13 Zinc octoate 400 0.0300 Low 14 Ionic surfactant (WITCOLATE AM) 100 0.0074 213.7 15 Ionic surfactant

(WITCOLATE AM) 400 0.0292 91.8

  16 Non-ionic surfactant (Tergitol 15-S-9) 500 0.036 84.6 17 HCl 487 0.037 Low 18 Triethylamine 32 0.0024 Low 19 Triethylamine 10 0. 00076 Low Triethylamine 100 0.000076 Low 21 Triethylamine 4 0 .00032 Moderate 1 Extraction carried out under nitrogen

  2 Test carried out using a Cannon-Fensky tube at 25 C.

  Low = about 35-74 mm2 / s; moderate = about 75-100,000 mm2 / s;

gel = about "100,000 mm2 / s.

- 18 -

EXAMPLES 2 TO 21

  As can be seen in Table 1, various compounds were added to the hydrolyzate of Example 1

  quantities. Both the type of compound and the amount added

  have an effect on the viscosity of the product. This shows

  the synergistic combination of silylacrylate and silica col-

loïdal with the chosen compound.

EXAMPLES 22 TO 27

  Sodium acetate was added in various amounts

  tities with the hydrolyzate prepared according to Example 1. The acetate

  sodium was added at different times during the form-

  mation of the product, which shows that the order of addition is not decisive. The results are given in the

table 2.

- 19 -

Table 2

  Quantity Quantity (g / 161.2 g (ppm per hydrolyzate 1 2 Ex. Product compound) at 24.2%) Viscosity 'Remarks 22 Na acetate 213 0.016 40.1 Partial devolatilization before addition of NaOAc (213 ppm / final product)

  23 Na 200 acetate 0.015 45.6 No devolatilization

  tion before addition of NaOAc (200 ppm / final product)

  24 Na acetate 100 0.0074 38 Devolatilization by-

  before adding NaOAc (100 ppm / final product)

  Na acetate 100 0.0074 49 No devolatilization

  tion before addition of NaOAc (100 ppm / final product)

  26 Na 200 acetate 0.016 38.5 Sequential addition

  tielle-100 ppm NaOAc immediately

before devolatili-

sation and 100 ppm after a certain

time of devolatili-

station. 27 Witness O O Gel

  1, 2 Test carried out as in table 1.

- 20 -

  It is understood that the above description has not

  has been given by way of illustration and not limitation and that all variants and modifications may be made thereto

  without thereby departing from the general scope of the present invention, as defined in the appended claims.

Claims (10)

  1. Curable, gel-free coating composition based on Si-   lice and acrylates characterized in that it comprises a chosen compound   in the group consisting of soluble salts, soaps, amines, surfactants   nonionic and anionic acids, acids, bases and mixtures thereof.   2. Method for curing the coating composition in accordance with composition 1, characterized in that it comprises the application of said composition to a substrate, and the exposure of said substrate to a source   sufficient energy to cause hardening.   3. Curable coating composition according to claim   1, characterized in that said compound is sodium acetate.   4. Process for the preparation of a cured coating composition   wheat, freeze-free, based on silica and acrylates, characterized in that it comprises:   the addition of a compound selected from the group consisting of soluble salts   wheat, soaps, amines, nonionic and anionic surfactants,   of acids, bases and mixtures thereof, to a coating composition   curable based on silica and acrylates.   5. Method according to claim 2, characterized in that said   the coating composition further contains a photoinitiator which   takes the exposure of said substrate to a UV light source.   6. Method according to claim 5, characterized in that said   photoinitiator includes methyl benzoylforrniate.   7. Method according to claim 4, characterized in that said coating composition contains a mixture of diacrylates and acrylates   polyfunctional with a ratio of diacrylates to polyfunctional acrylates-   between 0.5: 99 and about 99: 0.5.   8. A curable coating composition, free from gel, based on silica and acrylates according to claim 1, characterized in that said silica and acrylates comprise a silyl acrylate of formula (R) R2 O R2   (0) I a I2 311 2) (R'O) 4_abSi (C (R) 2CHR OC-C = (R2)) b an acrylic monomer of formula (2) 2 2 il ((2) (R) 2C = CR -C-0) R4   and colloidal silica, in which each R represents independently   ment a monovalent organic radical in C113, each R ′ represents inde-   while a C18 alkyl radical, R2 is chosen from hydrogen, R or mixtures thereof, each R3 independently represents a radical   C1_8 alkylene, each R4 independently represents an organic radical   that mono-or polyvalent, a is an integer between 0 and 2, b is an integer between 1 and 3, the sum of a + b being equal to 1 3, and n   is an integer between 1 and 6.   9. Coating composition according to claim 8, character-   in that said coating composition contains a mixture of polyfunctional diacrylates and acrylates with a ratio of diacrylates   polyfunctional acrylates between 0.5: 99 and about 99: 0.5.   10. Method according to claim 7, characterized in that said compound is sodium acetate.